The present invention relates generally to solder compositions, and more particularly to solder compositions useful for attaching a die to a substrate or package.
In one aspect, a method is disclosed herein for attaching an electronic component, such as a die, integrated circuit, or the like, to a substrate or package, comprising the steps of providing an electronic component and a substrate to be connected to each other across first and second surfaces with a liquid solder composition, and, in any order, either simultaneously or consecutively (a) contacting the first and second surfaces with the liquid solder composition, and (b) contacting the liquid solder composition with a freezing agent, wherein the liquid solder composition has a maximum melting temperature Tm1 of less than about 100 C. before it is exposed to the freezing agent, and wherein the liquid solder composition interacts with the freezing agent to form a second composition which has a maximum melting temperature Tm2, wherein Tm2xe2x88x92Tm1 is at least about 25xc2x0 C. The liquid solder composition is preferably an alloy containing Ga, In, and Sn, and preferably has a melting temperature of less than about 75 C., more preferably less than about 50 C., and most preferably less than about 25 C. Preferably Tm2xe2x88x92Tm1 is at least about 50 C., more preferably Tm2xe2x88x92Tm1 is at least about 75 C., even more preferably Tm2xe2x88x92Tm1 is at least about 100 C., and most preferably, Tm2xe2x88x92Tm1 is at least about 125 C. The freezing agent may be a material such as, for example, gold, which may be plated onto one or both of the first and second surfaces.
In another aspect, a method is disclosed herein for attaching a die to a substrate, comprising the steps of providing a die having a first faying surface thereon, providing a substrate having a second faying surface thereon, said second faying surface comprising gold, applying a gallium-based liquid solder composition to at least one of the first and second faying surfaces, and bringing the first and second faying surfaces into sufficient proximity such that the liquid solder composition is in contact with the first and second faying surfaces. The liquid solder composition is preferably applied to only the first faying surface prior to the point at which the first and second faying surfaces are brought into sufficient proximity such that the liquid solder composition is in contact with the first and second faying surfaces. Preferably, the liquid solder composition contains X % by weight Ga, Y % by weight In, and Z % by weight Sn, based on the total weight of the alloy, wherein 0 less than X,Y,Z less than 100. More preferably, X is within the range of about 40 to about 80, Y is within the range of about 5 to about 25, and Z is within the range of about 10 to about 30. The gold on the second faying surface is adsorbed by the liquid solder composition, and acts as a freezing agent for the composition.
These and other aspects are described in further detail below.